1. Field of the Invention
The present invention relates to a semiconductor integrated circuit, a magnetic detecting device, an electronic compass, and an ammeter, particularly, technique suitably used for a flux-gate magnetic sensor.
2. Description of the Related Art
As a magnetic field detection sensor, a flux-gate magnetic sensor is used which utilizes the shift of the B-H characteristics of a magnetic core having high magnetic permeability, which is caused by an input magnetic field, and the flux-gate magnetic sensor has resolution capability greater than a magnetic sensor using a hall device, a magnetoresistance element, or the like, and has the characteristics excellent in temperature stability.
The flux-gate magnetic sensor receives an external magnetic field such as geomagnetism or the like as an input magnetic field and is provided with a magnetic-field detection unit detecting the magnitude of the input magnetic field.
As such magnetic-field detection unit, a magnetic-field detection unit is known which is constituted of, an example, a magnetic core, an excitation coil which is wound around the magnetic core and excites the magnetic core, and a detecting coil (pick-up coil) which is wound around the magnetic core and detects the induced voltage depending on magnetic variation inside the magnetic core (refer to Japanese Unexamined Patent Application, First Publication No. 2005-147947, Japanese Unexamined Patent Application, First Publication No. H09-152473, and G. Trenkler: “Die Messung schwacher magnetischer Felder mittels Magnetometer mit direkter Zeitverschlusselung”, Messtechnik, 205, (1970)).
In the foregoing flux-gate magnetic sensor, a method is proposed which supplies a triangular wave current with the excitation coil, and measures, by a counter, the time interval in which a spike-shaped voltage waveform (pickup waveform) is generated when the magnetic flux in the magnetic core is reversed at the time of supplying the current.
Since the spike-shaped voltage waveform shifts on the time axis depending on the presence or absence of the intensity of the measured magnetic field (external magnetic field) of the environment in which a sensor is disposed, it is possible to detect the measured magnetic field by use of the time interval at which the waveform is detected.
The above-described method excites the core of the magnetic body by applying the excitation current having a triangular wave, when the phase applying the maximum value of the output voltage appearing in the pick-up coil is varied depending on the measured magnetic field, detects the phase difference (time difference) of the varied positive and negative peak voltages, and converts it into the values of the measured magnetic field.
Furthermore, phase detection is started in synchronization with the point at which the absolute value of the excitation triangular wave becomes maximum, that is, for example, the excitation waveform reaches the peak point.
However, in the voltage appearing in the pick-up coil, the variation of temporal differentiation in density of magnetic flux in the core of a magnetic body is detected. Therefore, at the region close to the position at which the absolute value of the excitation triangular wave is the maximum value and the variation of temporal differentiation is low in the excitation triangular wave, the absolute value of the pickup voltage decreases.
Consequently, regarding variation in the phase difference with respect to the measured magnetic field, the linearity of sensor output deteriorates at the region close to the position at which the absolute value of the excitation triangular wave becomes maximum.
Particularly, in the case where the operating time of the counter is represented by a dynamic range, sensor output linearity at both ends of the dynamic range deteriorates in accordance with deterioration in linearity at the region close to the position at which the absolute value of the excitation triangular wave becomes maximum.